Don't be alarmed if that glass ledge on Willis Tower makes a cracking sound. It's normal.

At the top of the nation's second-tallest building, the Willis Tower in Chicago, sightseers standing on glass suspended 1,353 feet over streets shouldn't be alarmed if they hear cracking.

That was the message from Willis Tower officials after some visitors said they heard cracking Wednesday night.

Ledge

Richard Derk / Los Angeles Times /

The Ledge at Chicago's Willis Tower seen soon after its opening. The attraction includes glass boxes that extend 4.3 feet out from 103rd floor Skydeck and provide a unique viewing experience.

The Ledge at Chicago's Willis Tower seen soon after its opening. The attraction includes glass boxes that extend 4.3 feet out from 103rd floor Skydeck and provide a unique viewing experience. (Richard Derk / Los Angeles Times /)

"I had my palms on the floor, and I could feel it cracking," visitor Alejandro Garibay, 23, of Stockton, Calif., told the Chicago Tribune, explaining that he was leaning down for a picture pose. "Honestly, I was in shock, in disbelief. I was scared."

"One of the craziest feelings I had in my life," added his cousin Antonio Saldana. "I thought I was going to fall through."

The pane of glass on the 103rd-floor area known as the Ledge is coated to prevent scratches, officials told the Tribune. When someone scratches the glass, it's normal for the coating to crack.

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